In the field of wireless communication, there is a growing demand for a broadband wireless access system that can efficiently perform high-speed, high-volume communications. In next generation systems, use of frequency scheduling is proposed to improve the frequency efficiency and thereby to increase the throughput. In such a system, an available broad frequency band is divided into multiple frequency resource blocks each of which includes one or more subcarriers. The frequency resource blocks are also called frequency chunks. Each mobile station is allocated one or more frequency resource blocks. In a frequency scheduling method, to improve the transmission efficiency or the throughput of the entire system, the base station allocates frequency resource blocks preferentially to mobile stations in good channel conditions based on channel quality indicators (CQIs) sent from the mobile stations for the respective frequency resource blocks of the downlink pilot channel.
FIG. 1 is a graph showing channel quality indicators of mobile stations A and B on a frequency axis. The graph also shows frequency resource blocks 1 and 2. In FIG. 1, for the frequency resource block 1, the mobile station A is in a better channel condition than the mobile station B; and for the frequency resource block 2, the mobile station B is in a better channel condition than the mobile station A. In this case, the throughput of the entire system can be maximized by allocating the frequency resource block 1 to the mobile station A and the frequency resource block 2 to the mobile station B.
Meanwhile, in a method shown in FIG. 2, the number of incoming waves from the transmitting end to the receiving end is intentionally increased to achieve multipath diversity and thereby to improve the channel quality. Such a method is called delay diversity or cyclic delay diversity (CDD). As shown in FIG. 2, in a delay diversity scheme, delay elements are provided in signal paths so that the same signal is sent from multiple transmitting antennas at different timings.
Also, technologies combining frequency scheduling and delay diversity are proposed, for example, in non-patent documents 1 and 2.
[Non-patent document 1] Samsung, R1-051046, “Further details on adaptive cyclic delay diversity scheme”, 3GPP TSG RAN WG1 meeting 42bis, San Diego, USA, 10-14 Oct., 2005
[Non-patent document 2] Samsung, R1-051047, “System performance of adaptive cyclic delay diversity scheme”, 3GPP TSG RAN WG1 meeting 42bis, San Diego, USA, 10-14 Oct., 2005